1. Field of the Invention
The present invention relates to medical devices for repairing tissue and more specifically to devices which facilitate tissue regeneration and to surgical methods for the implantation and fixation thereof.
2. Description of the Related Art
Various parts of the human body are comprised of fibrocartilage. Fibrocartilage forms the disc, meniscus, and labrums, located in the spine and temporo-mandibular joint, knee, and shoulder and hip, respectively. Additionally, fibrocartilage is present in other parts of the human body, such as fingers, wrists, and ankles. Fibrocartilage is a resilient, compressive tissue capable of accepting and withstanding high loads imparted during bodily movement. Generally, fibrocartilage is found between two adjacent bones, such as the locations set forth hereinabove.
The fibrocartilage of the knee forms menisci 10, 11, shown in FIG. 1. Menisci 10, 11 are semi-lunar, wedge-shaped portions of tissue that sit atop the tibia and articulate with the tibia and femur during movement of the tibia and/or femur relative to one another. Menisci 10, 11 have top articulating surfaces 12 which interface with the femoral condyle and bottom articulating surfaces (not shown) which interface with tibia plateau 14. Menisci 10, 11 function as shock absorbers between the femur and the tibia to distribute compressive and shear loads from the curved condyles of the femur to the relatively flat plateau of the tibia. While much of menisci 10, 11 can be classified as avascular and aneural, each menisci 10, 11 has three distinct zones of vascularity, shown in FIG. 2, red zone 16, red/white zone 18, and white zone 20. Red zone 16, comprised of approximately the outer peripheral third of each meniscus, is rich in blood supply and is highly vascular. White zone 20, comprised of approximately the inner peripheral third of each meniscus, is completely void of blood supply and is avascular. Red/white zone 18, comprised of the area between the red zone and white zone, has some limited vascularity with limited blood supply. As a patient ages, the size of the white zone 20 will increase and the size of red zone 16 and red/white zone 18 will correspondingly decrease.
Due to the high stress imparted on fibrocartilage, injuries and pathologies can occur in the fibrocartilage which are manifested in the form of tears, such as tear 22 shown in FIG. 3, defects, and/or degeneration. Tears may occur due to the existence of prior defects in the fibrocartilage, shear loading of the fibrocartilage, and/or compounded loading resulting from repetitive compressive loading occurring over a period of time. Additionally, fibrocartilage can deteriorate as a result of aging, resulting in hard and/or soft areas which further facilitate the creation of tears therein.
One common procedure for treating fibrocartilage tears is to surgically remove part or all of the fibrocartilage surrounding the tear, such as removing a portion of the meniscus. These procedures, known as meniscectomies or partial meniscectomies when performed on the meniscus, are commonly utilized in the case of “unrepairable” or complex tears such as radial tears, horizontal tears, and vertical longitudinal tears occurring outside the vascular zone. Additionally, these procedures may be performed when there is fibrillation and/or degeneration caused by defects in an avascular or limited vascular area, since these injuries are unlikely to heal. As shown in FIG. 4, a partial meniscectomy may be performed in which the meniscus is removed along lines extending inwardly toward the inner meniscus from the peripheral ends of tear 22. In some cases, implants may be inserted to replace the portion of the meniscus removed during the procedure. Meniscectomies, and similar fibrocartilage procedures, typically provide immediate pain relief and restoration of knee function to a patient. However, cartilage wear on the condylar or tibial plateau surfaces and the eventual development of osteoarthritis may occur as a result of the meniscectomy. Additionally, the onset of osteoarthritis may lead to more chronic conditions resulting in the need for a total knee replacement procedure.
Another method for treating fibrocartilage tears, including tears of the meniscus, is to attempt to surgically repair the torn tissue. This technique is most commonly performed when the tear is a longitudinal vertical tear located in the vascular area of the fibrocartilage, such as red zone 16 of meniscus 10, shown in FIG. 2. To facilitate tissue regeneration, the tear walls may be rasped or trephined to induce bleeding. Additionally, the tear walls may be stabilized with sutures or other retention devices.
A further method for treating fibrocartilage tears is the subject of U.S. patent application Ser. No. 10/558,926 to Schwartz (“Schwartz '926”). The stent of Schwartz '926 is designed with an interior, longitudinally-extending bore and external threads or ribs. Stent 24, shown in FIG. 6, is inserted through fibrocartilage tissue and positioned to extend across walls 26, 28 of fibrocartilage tear 22, shown in FIG. 5, to secure the sides of the tear together. The threads or ribbing of stent 24, denoted by slanted, dashed lines in FIG. 6, effectively retain the stent, and corresponding tear walls 26, 28, in position. Additionally, the outer wall of stent 24 includes a plurality of apertures, not shown, extending from the interior of the longitudinal bore to the exterior surface of stent 24. These apertures allow for the dissemination of blood, biological factors, and cells from stent 24, as blood, biological factors, and cells flow through stent 24 from a vascular region of the fibrocartilage to a semi-vascular or avascular tear region of the fibrocartilage. The dissemination of blood, biological factors, and cells via stent 24 stimulates tissue regeneration. While the device disclosed in Schwartz '926 is effective, the walls of the fibrocartilage tear may actually be pushed apart during implantation of the stent and prevent effective healing of the tear. Additionally, even when the sides of the tear are properly aligned, the tear walls may loosen or migrate over time. Further, the blood dissemination apertures in the stent may not be as effective in providing maximum blood flow to the area of interest as desired to effect healing.
What is needed is a device that is an improvement over the prior art.